The present invention relates to an electrophotographic image forming apparatus provided with a pre-transfer charger.
Some electrophotographic image forming apparatuses are provided with an image bearing element, a primary transfer element, an intermediate transfer element, and a secondary is transfer element. On the surface of the image bearing element, an electrostatic latent image is formed by using image data, and the electrostatic latent image is developed into a toner image. The primary transfer element primarily transfers the toner image formed on the image bearing element to the intermediate transfer element. The secondary transfer element secondarily transfers the toner image from the intermediate transfer element onto a sheet of paper.
A device as disclosed in Japanese Patent Laid-Open Publication No. 2010-14995 as the conventional image reading device is provided with a pre-transfer charger. The pre-transfer charger applies applied voltage with a polarity opposite to a polarity of a charged toner image to the intermediate transfer element. The charged state of the toner image that has been primarily transferred to the intermediate transfer element is stabilized to improve secondary transfer efficiency, thus preventing the toner from remaining on the secondary transfer element, which can become a cause for dirt on the reverse side of a sheet of paper during subsequent image forming processes.
However, the image forming apparatus disclosed in Japanese Patent Laid-Open Publication No. 2010-14995 cannot stabilize the charged state of the toner image formed on the intermediate transfer element corresponding to a portion to which the residual toner adheres when the residual toner adheres to the pre-transfer charger. In the portion in which the charged state of the toner image is not stable, a white streak is formed in the sheet of paper that has been subjected to an image forming process because the toner image is not transferred to the portion. The white streak is not easily visible, so that a user will often miss that the pre-transfer charger is dirty.
In view of the foregoing, an object of the present invention is to provide an image forming apparatus capable of detecting the presence of dirt of a pre-transfer charger, as well as a cleaning method of the pre-transfer charger.